Re: [PATCH] MIPS: fix pmd_mkinvalid

From: Hongchen Zhang
Date: Tue Jul 12 2022 - 06:01:16 EST

On 2022/7/7 下午7:12, Hongchen Zhang wrote:
On 2022/7/7 下午5:22, Thomas Bogendoerfer wrote:
On Thu, Jul 07, 2022 at 04:11:35PM +0800, Hongchen Zhang wrote:
When a pmd entry is invalidated by pmd_mkinvalid,pmd_present should
return true.
So introduce a _PMD_PRESENT_INVALID_SHIFT bit to check if a pmd is
present but invalidated by pmd_mkinvalid.

What problem are you trying to fix ? What are the symptoms ?

Reported-by: kernel test robot <lkp@xxxxxxxxx>

the test robot showed problems with your last version of the patch,
which hasn't been integrated into at least the MIPS tree, so no
need to that.


Hi Thomas,
  The idea come from the commit:
  b65399f6111b(arm64/mm: Change THP helpers to comply with generic MM  semantics).
  There is an problem now:
        CPU 0        CPU 1
    pmdp_invalidate        do_page_fault
    ...              __handle_mm_fault
                    is_swap_pmd == true
                    trigger VM_BUG_ON() ?
  the reason is that pmd_present return true,after this commit
  pmd_present will return false,and the VM_BUG_ON will not be triggered.
  Like arm64 does,we can introduce a new bit to fix this.

Hi Thomas,
Is there problem of this patch? What's your opinion of this patch?